1. Field of the Invention
The present invention relates to a video display device suitable for application to a large video display device or the like. Specifically, the present invention relates to a video display device wherein a memory stores previously current correction values for correcting variations in luminous brightness of a plurality of display elements constituting a video display part, and the variations in luminous brightness within the video display part can be corrected by driving the display elements through the use of the current correction values read from the memory.
2. Description of Related Art
A large video display device has been set up in a place for doing various events outdoors, an outdoor or indoor stadium, sport facilities, and so forth. The large video display device displays the contents of events, the results of competition, and so forth on a large-sized video display part (i.e., a panel or a screen) thereof.
The video display device for this purpose has a video source (i.e., a VTR or the like) 12, as shown in FIG. 1. The video source 12 transmits video images (the contents of events, the contents of competition, drama programs, and so forth) to a signal processing device 30 where they are converted into signal form suitable for a video display part 14. Thereafter, the signal processing device 30 transmits the converted signal to the video display part 14 and then a desired image or picture is displayed on the video display part 14. The video display part 14 is constructed so as to be suitable for a large screen (e.g., 4m.times.3m).
The video display part 14 is a collection of a plurality of dots. FIGS. 2A through 2C show an example thereof. In the example, a unit dot (hereinafter called "dot") 16 comprises a trio of display elements, each of which emits light of red R, green G or blue B, as shown in FIG. 2A. The dots 16 are arranged over p rows and q columns (both p and q are four in the illustrated example) to form each individual unit cell 18 (see FIG. 2B). Further, the unit cells are arranged over m rows and n columns (both m and n are four in the illustrated example) to form a display unit 20 as a unit (see FIG. 2C). A large video display part 14 is constructed by a collection of the display units 20.
In such a video display part 14, separate drivers drive respectively the display elements themselves defined as an RGB trio constituting the dot 16 in order to obtain sufficient luminous brightness, for example. The unit cell 18 is normally formed by 16 dots (4.times.4 dots) and thus forty eight individual drivers drive forty eight display elements (16 dots.times.3 elements).
Even if each unit cell is represented as 4.times.4=16 dots as shown in FIG. 3, forty eight drivers corresponding to forty eight display elements cause a drive circuit to increase in size. As means for solving this, means have been proposed for reducing the number of drivers to 1/2 of the number by providing switching or selector means such that one driver drives two display elements.
FIG. 4 is a fragmentary systematic diagram showing one example of the proposal. When one unit cell consists of forty eight display elements as shown in FIG. 3, a driver circuit 32 is constructed so as to drive twenty-four display elements corresponding to 1/2 of the forty eight display elements. Thus, the driver circuit (IC driver) 32 comprises latch circuits 33a through 33x for latching twenty for video data S0 through S23 and drivers 34a through 34x electrically connected to the latch circuits at their subsequent stages as shown in FIG. 4. Each of the respective drivers 34a through 34x is respectively connected to their corresponding display elements RU0 through BL7 via switching means 35 and then the driver circuit 32 transmits the outputs of drivers 34a through 34x to the display elements RU0 through BL7.
In the unit cell as shown in FIG. 3, eight dots of an n row and an n+2 row (i.e., a lower-stage dot group L) are simultaneously driven. Next, eight dots of the remaining n+1 row and n+3 row (lower-stage dot group L) are also simultaneously driven. That is, these dot groups, i.e., display element groups U and L, are alternately driven in a predetermined cycle. Here, each set of the display elements RU0 through RU7, GU0 through GU7 and BU0 through BU7 emits respectively the same light-emitting color. Similarly, each set of the display elements RL0 through RL7, GL0 through GL7 and BL0 through BL7 emits respectively the same light-emitting color.
An example of the alternate driving of the dot groups U and L will be shown in FIGS. 5A through 5C. These figures show the case in which they are alternately switched over plural times (about 16 times) at time intervals (each corresponding to 1/30 second) of individual one frame. During this period of time for one frame, the same video data is supplied to the corresponding display element group.
On the other hand, when the video display part 14 comprises the plurality of display elements, as described above, such as light-emitting diode devices (LEDs) the luminous brightness of each individual element varies, although dissimilar even according to the display element to be used. It is therefore necessary to correct previously current values for driving the display elements so that all the display elements to be used may be kept constant in luminous brightness.
As a current correcting method, adjustment of constants of the drivers for driving display elements is considered. In doing so, however, when a unit cell is replaced by another, the corresponding individual drivers must be re-adjusted so as to provide new current correction values for display elements provided within the replaced unit cell. This becomes so troublesome.
With the foregoing problems in view, it is therefore an object of the present invention to provide a video display device capable of easily setting current correction values for adjusting luminous brightness even when a unit cell is replaced by another.